Flow Mapping (Box Shaped World)

[Editor's note: Flow maps have always ranked high on my radar but constructing them has always been tedious. This post and academic paper link detail how they can be automated with programatically, including edge routing (not directly from A to B, but with bends to not overlap other connections).]

Getting a head start on a new project that is more cartographic. It will involve mapping migration/flows from Australia to the Northern Territory (probably smaller geographic units than states). I like making maps, and so I’m excited to do some cartography beyond standard ArcGIS layouts. There are different possibilities on how to map this. Initially, I think I will use something like this that creates a more trunk/branch flow map instead of the typical straight line between places (Tobler’s Flowmapper). The project lead doesn’t like this style too much, but thought the trunk/branch style might work. We might pursue other mapping techniques, which would be cool to try and apply different map techniques to this area…

Cartographers have long used flow maps to show the movement of objects from one location to another, such as the number of people in a migration, the amount of goods being traded, or the number of packets in a network. The advantage of flow maps is that they reduce visual clutter by merging edges. Most flow maps are drawn by hand and there are few computer algorithms available. We present a method for generating flow maps using hierarchical clustering given a set of nodes, positions, and flow data between the nodes. Our techniques are inspired by graph layout algorithms that minimize edge crossings and distort node positions while maintaining their relative position to one another. We demonstrate our technique by producing flow maps for network traffic, census data, and trade data.